Conventionally, there has been proposed a vehicle headlamp which uses a light source having a plurality of semiconductor light emitting devices which are aligned (JP-A-2013-54993). This vehicle headlamp is configured to form light distribution patterns which illuminate predetermined ranges ahead of the vehicle. The light distribution patterns are each made up of a collection of a plurality of partial areas. The partial areas are illuminated by the corresponding semiconductor light emitting devices when they are illuminated or turned on. Thus, the plurality of semiconductor light emitting devices are individually controlled so as to be turned on or off to form various light distribution patterns. In this configuration, for example, in case a preceding vehicle is detected in one partial area of the plurality of partial areas, the semiconductor light emitting device which corresponds to that particular partial area can be turned off so that the partial area can be put in an unilluminated state to thereby restrict the driver of the preceding vehicle from being dazzled.
Incidentally, in the event that the partial areas of a light distribution pattern are illuminated or unilluminated, a certain length of switching time becomes necessary to illuminate the semiconductor light emitting device to target brightness or turn off the devices or dim them. Although there are various ways of changing the brightness, it is one of ideas to be taken to change the brightness by a constant ratio at all times because the switching control of light distribution patterns and the drive circuit configuration of light emitting devices can be simplified.
However, in the event that the brightness of a plurality of areas is changed individually according to situations, depending upon the brightness of the semiconductor light emitting devices before the change or target brightness to which the semiconductor light emitting devices are illuminated, the time required for the individual areas to reach their target brightness (the switching time) differs. Because of this, depending upon situations where light distribution patterns are changed, the driver may feel the sensation of physical disorder.